The present invention relates to a new improved substantially solvent-free process for preparing phthalate-moiety based polyesterimide resins, to new resins prepared by the process, and to substrates (e.g. electrical conductors) coated with compositions comprising the new resins.
Polyesterimide (PESI) resins have typically heretofore been prepared from phthalate-moiety-contributing compounds (e.g. lower dialkyl esters of terephthalic or isophthalic acid) using syntheses wherein inert solvents are employed. As used herein, "inert solvents" and terms of similar import mean solvents which do not react with monomeric reactants from which PESI resins are synthesized. Thus, PESI resins have been synthesized by heating, in the presence of inert solvents (e.g. cresol) reaction mixtures of phthalic acid lower dialkyl ester with diol, triol, diamine and carboxylic acid anhydride having an additional carboxyl group. Such solution syntheses have not been entirely satisfactory due to high cost of the solvents and increasingly stringent governmental regulations on emission and disposal thereof.
Attempts to carry out such PESI synthesis in the absence of inert solvents have not been entirely satisfactory in that the lower alkyl phthalate esters undergo sublimation from the reaction mixtures resulting in deposition of flow-hindering solid deposits in conduits provided for recovering by-product vapors released from the reacting mixtures, deviations from the preselected relative amounts of reactants in the reacting mixtures, and other problems. Moreover, we have found that in the absence of a solublizing amount of inert solvent, rapid increases in resin viscosity (i.e. molecular weight) in later stages of the synthesis undesirably occur. This creates additional control problems including, in some instances, gelling of the resin in the synthesis vessel.
Precopio et al, U.S. Pat. No. 2,936,296, discloses a process for preparation of polyester resins from, e.g., dimethyl terephthalate (DMT), ethylene glycol (EG), and a saturated aliphatic trihydric alcohol, wherein the reaction is carried out with xylene or a similar material added to the reaction mixture for the stated purpose of preventing sublimation of DMT. As described therein, the added material (e.g. xylene) takes no part in the reaction. George et al, U.S. Pat. No. 3,297,785, discloses modified polyester resins and broadly suggests that unsaturated alcohols, e.g. allyl alcohol-glycol maleates, may be utilized in modifying their polyesters.
PESI polymers and processes for synthesis thereof are described in the following representative U.S. Pat. Nos.: 3,382,203 (Rating et al), 3,426,098 (Meyer et al), 3,853,817 (Weddleton), 3,931,418 (Riskin) and 4,038,254 (Schade et al). The Risken patent further discloses (at column 2, line 57-60) that up to 25% of the ester groups of their resins may optionally be replaced by acid amide groups by replacing some of "the" alcohols with amino alcohols or polyamines and indicates (in the paragraph bridging column 5 and column 6) that such amines (e.g. including ethanolamine) can be reacted with carboxyl groups available for esterification to form acid amide compounds.
Keske et al, U.S. Pat. No. 4,045,407, describes a process for preparing polyamideimides which comprises reacting a composition comprising an aromatic diprimary amine and a tricarboxylic acid compound in an alcoholic solvent comprising a monohydric alcohol containing from about 4 to 10 carbon atoms. As therein described, (1) where only a diprimary aromatic amine is reacted, a tertiary amine is required in the alcoholic solvent, (2) if a glycol is employed, it can be present in an amount up to 15% of the total amount of glycol and alkanol, and (3) the total concentration of alkanol, glycol and tertiary amine comprises 20 to 75% of the reaction mass. Each of the patents cited above is incorporated herein by reference.
However, the prior art did not recognize that, as it has now been found by practice of the present invention, the foregoing and other problems in solventless synthesis of PESI resins can be eliminated to a substantial extent by a new improved synthesis process wherein there is included in the reaction mixture an organic component containing monohydric alcohol functionality. The monohydric alcohol may contain other functional groups, e.g. oxy, alkoxy, etc., but preferably is free of other functional groups which react with carboxyl groups to form esters, acid amides, etc. It has also now been found that PESI resin products prepared by the process of this invention exhibit substantially improved stability against premature curing for prolonged periods of time.